package main.practices.algorithmCourse.hash;

import java.util.*;

/**
 * @Description:
 *               Design a data structure that supports all following
 *               operations in average O(1) time.
 *
 *               insert(val): Inserts an item val to the set if not already
 *               present.
 *               remove(val): Removes an item val from the set if present.
 *               getRandom: Returns a random element from current set of
 *               elements. Each element must have the same probability of
 *               being returned.
 *               Example:
 *
 *               // Init an empty set.
 *               RandomizedSet randomSet = new RandomizedSet();
 *
 *               // Inserts 1 to the set. Returns true as 1 was inserted
 *               successfully.
 *               randomSet.insert(1);
 *
 *               // Returns false as 2 does not exist in the set.
 *               randomSet.remove(2);
 *
 *               // Inserts 2 to the set, returns true. Set now contains
 *               [1,2].
 *               randomSet.insert(2);
 *
 *               // getRandom should return either 1 or 2 randomly.
 *               randomSet.getRandom();
 *
 *               // Removes 1 from the set, returns true. Set now contains
 *               [2].
 *               randomSet.remove(1);
 *
 *               // 2 was already in the set, so return false.
 *               randomSet.insert(2);
 *
 *               // Since 2 is the only number in the set, getRandom always
 *               return 2.
 *               randomSet.getRandom();
 * @Author: shenpeng
 * @Date: 2020-03-06
 */

public class RandomizedSet {

    List<Integer> list;

    Set<Integer> set;

    /** Initialize your data structure here. */
    public RandomizedSet() {
        list = new ArrayList<>();
        set = new HashSet<>();
    }

    /**
     * Inserts a value to the set. Returns true if the set did not already
     * contain the specified element.
     */
    public boolean insert(int val) {
        if (!set.contains(val)) {
            set.add(val);
            list.add(val);
            return true;
        } else {
            return false;
        }
    }

    /**
     * Removes a value from the set. Returns true if the set contained the
     * specified element.
     */
    public boolean remove(int val) {
        if (set.contains(val)) {
            set.remove(val);
            List<Integer> newList = new ArrayList<>();
            newList.add(val);
            list.removeAll(newList);
            return true;
        }
        return false;
    }

    /** Get a random element from the set. */
    public int getRandom() {

        int index = new Random().nextInt(list.size());
        return list.get(index);
    }
}

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * RandomizedSet obj = new RandomizedSet();
 * boolean param_1 = obj.insert(val);
 * boolean param_2 = obj.remove(val);
 * int param_3 = obj.getRandom();
 */
